Apparatus for maintaining constant hydrostatic pressure upon a liquid



Nov. 21? 19 39. c. M. FIELD S ET AL 03 APFARATUS FOR MAINTAINING CONSTANT HYDRQSTATIC PRESSURE UPON A LIQUID Filed Feb. 3, 193a" III) Char/es MfIb/dr (v Reuben 7 Fz'eldr INVENTORS M. A from V5) Patented Nov. 21, 1939 APPARATUS FOR MAINTAINING CONSTANT HYDROSTATIC PRESSURE UPON A LIQ- UID Charles M. Fields and Reuben T. Fields, Arlington, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application February a, 1938, Serial No. 188,466

2Claims.

This invention relates to an apparatus for maintaining substantially constant hydrostatic pressure upon a liquid contained in a vessel of fixed volume during contraction in volume of the 5 liquid in the vessel and, more particularly, relates to an apparatus for keeping a mold completely filled with a polymerizable organic liquid compound during the polymerization of such liquid and, also, maintaining a substantially constant hydrostatic pressure upon the liquid in the mold during the polymerization.

In C. M. Fields United States Patent 2,057,674, entitled Polymerization process, is described the polymerization ofv polymerizable organic liquids. In general, this polymerization is carried out in a mold or vessel of fixed volume, polymerization being commenced at one closedend of the mold, usually the bottom, and the zone of polymerization is moved gradually to the opposite end of the mold as the polymerizable liquid is converted to solid polymer. The conversion of the polymerizable liquid to solid polymer is accompanied by appreciable shrinkage and, further,

there is a tendency toward the formation of bubbles in the polymerizing liquid due to local overheating of the liquid being polymerized. It has been found desirable both to prevent formation of 'voids due to shrinkage and bubbles'to maintain a pressure of the order of- 50-300 pounds per square inch on the polymerizable liquid in the' mold during polymerization; likewise, it is desirable to make use of the full volume of the vessel or mold employed and, to this end, to be able to introduce into the mold continuously throughout the polymerization additional polymerizable liquid to compensate for the shrinkage of the material undergoing polymerization in the mold.

Heretofore, various devices have been tried to I accomplish the two-fold purpose of keeping the mold continuously full of polymerizable liquid and maintaining a substantially constant pressure upon the liquid in the mold. These polymerizable organic liquids which are used either as straight monomer or, more generally, as a viscous syrup of polymer dissolved in monomer, are substantially devoid-of lubricating properties Because of this characteristic oi. theseliquids, the use of mechanisms having sliding metal-to metal contacts or stuffing boxes where the polymerizable 50 liquid has access, are unsatisfactory. No device heretofore tried has proven entirely satisfactory. I An object of the present invention is to provide "an apparatus capable of maintaining a substantially uniform hydrostatic pressure upon a liquid 55 contained in a vessel of fixed volume and undergoing contraction in volume and, at the same time, to keep the vessel filled by the introduction of further liquid. A more particular object of the invention is to provide such an apparatus capable of maintaining a substantially uniform hydrostatic pressure upon a polymerizable liquid undergoing polymerization in a constant volume mold while, at the same time, keeping the mold filled by the introduction of further polymerizable liquid. 10

A still further object of the invention is to provide an apparatus as above characterized in that:

(1) It shall not give rise to contamination of the polymerizable liquid;

. several hundred pounds per square inch upon the liquid in the mold, and require no accumulator; and (6) It shall keep the mold filled with polymerizable liquid at all times during the polymerization by feeding in liquid to compensate for the contraction in volume of the liquid in the mold as a result of its polymerization, i. e., it shall be capable of making a variable delivery of liquid against constant pressure and that it shall be ;-capable of doing this without .resort to a safety valve or other device for bleeding away excess pressure. I i I I A still further object is to provide an apparatus that is automatic in its action so that it functions without attention and without the need of shutting oil and restarting the mechanism'which activates it. A still further object is to provide a simple and readily operated accessory apparatus with which-to conduct processes of 'polymerization of polymerizable organic liquids in molds, such as the process disclosed in the above mentioned United States Patent 2,057,674. Other objects of the invention will be apparent from the I description given hereinafter.

The above objects are accomplished according to the present invention broadly by the use of an apparatus comprising a bellows pump, conduit means-connecting the bellows pump to a supply of liquid, said conduit means having a. check valve section, of an apparatus according to one specific embodiment of the present invention; and

Fig. 2 is a more or less diagrammatic view, in vertical section,.of a compressible connecting rod adapted for use in the apparatus illustrated in Fig. 1.

Referring to Fig. 1, reference numeral ll designates a cylindrical bellows member, preferably made of two-ply nickel plated brass, but other suitable metals or materials impervious to the liquid being handled will occur to those skilled in the art, closed at one end by a' piston I2 by soldering the end of the bellows member H mm the groove l3 cut' in the face of the piston l2. The other end of the bellows member H is similarly closed off by being soldered in a groove 13 cut in the lower face of the block H. To the block I4 is attached the cylindrical sleeve IS in which the piston l2 makes a sliding fit.

A cylindrical plug I6 is threadably mounted on the block I4 and extends into and fills most of the space within the bellows member H. The plug l6 must be smaller in diameter and length than, respectively, the minimum diameter and length of the interior of bellows member II, as assembled, to leave a space 20 for the passage of liquid within the bellows member II.

A conduit means connecting the interior space 20 of bellows member H with an outside source of liquid is provided by the intake port 18 drilled from the bottom of plug l6 through the plug l6 and through the block I and terminating in the coupling l1 for the attachment of a supply pipe. The ball check valve is is placed inv the port It to permit flow of liq 'd into the space 20 and to check flow of liquid in the opposite direction.

A second conduit means connecting the space 20 within the bellows member II to the vessel (not shown) in which the constant hydrostatic pressure is to be maintained, is provided by the discharge port 22 drilled through the block ll and terminating in the fitting 2| adapted to be connected with the aforementioned vessel. The port 22 leads into the space 20 between the bellows member I I and the outer wall of the plug I6, the plug 16 being tapered at24 to provide greater room for the opening of the port 22. The ball check valve 23 is placed in the port 22, to permit flow of liquid from the space 20 out through port 22 and fitting 2| but to check flow of liquid in the opposite direction.

To the underside of the piston I2 is connected by meansof the pin 25-4 the connecting rod or link 25 which, at its other end, is similarly connected by the pin 25-41 to the lever 28. This lever 26 is pivotally mounted on a shaft 21 journaled in the bearing block 28.

Removably'mountedon the lever 26 at the opposite end from connecting rod. 25, and preferably at several times greater distance from the ful-' crum of the lever 26 at 21-, are principal weight 23 and increment weights 29-4, 23-1), and

'29-'-c, all of them drilled through so as to he slipped over a pin 30 mounted on the lever 26..

Beneath the lever 26 at the end carrying the weights is a cam 3i keyed to a shaft 32 rotatably mounted in a bearing member 33. This shaft 32 is driven at a low sp ed, preferably from about 5 to R. P. M., by means of conventional motor and speed-reducing mechanism not shown in the drawing. cross section and is mounted eccentrically on the shaft 32.

Bearing members 23 and 33 are supported on a foundation member 34 which also supports the assembly including the sleeve [5 and block member H. The supporting structure for the sleeve l5 and block I have been omitted from the drawing for the sake of clarity.

A hole 35 is provided in the lever 26 at a convenient point along its length and through this hole 35 is passed an adjustable stop member comprising a bolt 36 mounted on the foundation member 34 and provided with a locknut 31.

- The operation of. the apparatus shown in Fig. 1 will now be described in connection with the polymerization process disclosed in said United-States Patent 2,057,674 as applied to the manufacture.

of rods, an'dthe like, o polymerized methyl methacrylate.

Conveniently;the cam 3|.is of circular The intake port i8 is connected, through the fitting l'l, with a supply of partially polymerized syrup of methyl methacrylate which is located at such a level that the syrup will fiow into the apparatus through the fitting IT. The shaft 32 .carrying the cam 3| is then set into rotation. The cam 3| is capable of raising the weighted arm of the lever 26 and, accordingly, as the maximum radius of the cam 3| comes into vertical position. above the bearing member 33, this arm of the lever 26 is raised to its highest position. correspondingly, the bellows member ll, being actuated through the connecting rod 25, traveling downwardly, is expanded longitudinally. This increases the volume of the space 20 within the bellows member II and there is thus drawn into the bellows member [I through the check valve I3 and the port IS, a quantity of the methyl methacrylate syrup.

As the cam 3| rotates to its other extreme position, the weighted arm of the lever 26 follows it downwardly, being actuated by the weight-23. This movement causes the piston [2 to rise and compress 'the bellows member II, thereby decreasing the volume of the space 20 within the bellows member II. The pressure thus produced upon the contents of the space 2; closes the check valve l3 and causes the check valve 23 to open for the discharge, at first, of air, but, ultimately, as the space 2| becomes filled by successive strokes of the piston rod 25, methacrylate syrup is discharged through theport 22, pastthe check valve 23 and into the fitting 2L2 The polymerized syrup, which is preferred for the process of polymerization, is of sufficient viscosity, and the diameter of the port I! is sufliciently'small, so that air initially contained in the port I! is pushed out ahead of the syrup, even vertically downward. Furthermore, the whole intake port ll, beginning at the fitting! 1, hasnopartinwhichaircanbetrappedandremain out of the line of flow pf the syrup; in particular, the horizontal portion of the port I. above the check valve I3 is free from crown or crevice in which air might become temporarily trapped.

An elongated mold of fixed volume, such as described in said United States Patent 2,057,674, is filled with methyl methacrylate syrup and, as soon as the syrup free from air beginsto issue from the fitting 2|, the filled mold is connected with this fitting, the connecting members being operating against the filled mold which is closed and of fixed volume. It therefore begins to build up hydrostatic pressure upon the liquid in the .mold and .the magnitude of such hydrostatic pressure is controlled by the magnitude of-the weight 29 which causes the hydrostatic pressure to. build up to a definite value and 'then maintains it at that value. Until this fixed value is reached each rotation of the cam shaft 32 causes a reciprocally vertical movement of the lever 26 because the weight 29, multiplied by its arm, is greater than v the back pressure transmitted through the connecting rod 25, multiplied by its arm, and the weight 29 goes down each time the cam 3| revolves.

Ultimately, the pressure within the mold and bellows system, sealed by the check valve I9, is builtup to the point at which it balances the downward thrust of-theweight 29. The weight 29 then does not move downward'with the next rotation of the cam, being held up by the downward thrust of this pressure, through the connecting rod 25, upon the opposite end of the lever 26. Actually, the weighted end of lever 26 does not remain balanced stationary in its extreme high position because any play inthe bearings and any'elasticity in the bellows member permits it to drop a little when the support of the cam 3| is withdrawn, but such drop is not sufficient to cause an opening of the valve 23 nor a corresponding opening of the check valve I9 when the weighted end of the lever 26 is again raised to its top position by the cam 3|.

upon the syrup in the mold cannot exceed the predetermined value controlled by the magnitude of the weight 29.- As long as this pressure is maintained, the cam rotates idly.

But the polymerization of the methyl methacrylate in the mold results in a contraction in volume of the methyl methacrylate in the mold. This contraction effects a decrease in the hydrostatic pressure upon the contents of the mold. The check valve 23 is caused to open by the greater pressurestill being maintained in the bellows member H by the downward thrust of the weight 29, and syrup is forced thereby from the space 2|] past the check valve 23. The resulting reduction in pressure within the bellows member permits it to be compressed by-the upward thrust of the connecting rod 25, the weighted arm of the lever 26 thus following the cam downward, and the .pressure building function of the appa ratus is thus resumed, continuing until'the hydro static pressure in themold has again been built up to the fixed value or maximum governed by the magnitude of the weight 29. v

It will be understood by those skilled inv the art that the apparatus of the present invention fixed volume but also to maintain this pressure ,flhispite of the contraction in volume of the ma- 't er ial'within, the mold as a result of the polymerization, though automatically feeding additional liquid into the mold in an amount sufli- In this' way the pressure .developedby the apparatus cient to maintain the pressure at the desired point.- While this feed is actually intermittent or pulsating, taking place only during the downward movement of the weight 29, yet, in actual practice, because of the elasticity of the mold, it has beenfound that the mechanism as described will build up and hold a hydrostatic pressure of, for example, 200, pounds per square inch with a fluctuation of not more than 5 pounds per square inch.

Two optional features of the apparatus as shown in Fig. 1 are a stop 38, conveniently a section of smaller inside diameter forming a part of the sleeve l5, and an adjustable stop member 36, 31. The purpose of both of these features is the same, namely, to limit the upward motion of the weighted arm of the lever 26 and, ordinarily, onlyone, rather than both, as shown, will be employed. Neither one functions so long as the proper weight 29 is in position upon the lever arm 26 but they serve as a safeguard at any time when the weight may be removed and during any period of operating the apparatus manually instead of by the cam.

In an alternate form of the apparatus of the present invention, the bellows member 'H and associated parts are employed with a compressibleconnecting member or rod, shown in- Fig. 2, in combination with any conventional means such as a crank pin for giving said compressible connecting member reciprocating motion. The connecting rod 25, lever 26, and cam 3|, with their associatedparts, 'shown in Fig. 1, are not employed in this modification.

Referring to Fig. 2, a bellows member 4|' is soldered to anupper plate 42 containing a port 43 which connects the interior 44 of the bellows member 4| through a pipe 45 to a source of gas pressure. The bellows member 4| is soldered at its lower end to a block 46 which is provided with the bearing hole 41 adapted to receive a crank pin, not shown, whereby. the block 46 may be given a regular reciprocating vertical motion.

The bellows member. and associated parts fit withina frame 48 carrying the vertical arm 49 provided with a-hole 50; By means of a connecting pin passing. through the hole 50 of arm 49, the compressible connecting member is adapted to be connected with the piston |2 (Fig. 1). The bellows member 4| and associated parts are vertically slidable within frame 48, which is cut away at 5| to accommodate the projecting pipe 45. Alternatively, and without. difference of function, the plate 42'can be rigidly mounted at the top of the frame 48, leaving the lower end of the bellows member 4| and the plate 46 attached thereto, vertically slidable within the frame 48'.

The mechanism of Fig. 2 is attached to the piston |2 (Fig. l) and the crank pin, not shown in the drawing, is inserted into the bearing hole 41. When suitable gas pressure is built up within the bellows member 4|, the latter is thereby lengthened and the block 42 is forced into contact with the top of the frame 48. With the crank pin in the bearing hole 41 in stationary position at or nearethe bottom of its stroke and holding the block 46 in fixed position, the lengthening of the bellows member 4| also causes the frame 48 to move upward until the block 46 abuts against downward the frame 48 and thus lengthens the bellows member N (Fig. 1), causing the intake upon the up stroke depends, however, upon the magnitude of the gas pressure within the bellows member 4|. Compression of the bellows member N (Fig. 1) with consequent opening of the valve 23, requires the application of a force suflicient to overcome the liquid pressure existing on the far side of the valve 23. If the gas pressure within the bellows member 4| is sufficiently high to prevent the compression of this bellows 4| under this minimum force, then the up stroke of the crank pin will elevate the frame member 48, compress the bellows member II and cause a discharge of liquid through the valve 23. If, however, the gas pressure within the bellows member 4| is not sufliciently great, then the up stroke of the crank pin will merely compress this bellows member 4|, so that its lower end, carrying the block 46, will move upward with respect to the frame 48, to such a position as is shown in Fig. 2, while the frame itself is not caused to rise, and there will be, correspondingly, no compression of the bellows member H and no discharge of liquid through the valve 23.

The amplitude of motion of the crank pin must, of course, be sufiiciently restricted so as to avoid damage to the bellows member 4| by too great compression.

l It is thus evident that against a given pressure in the vessel in ,which pressure is to be maintained constant, which is not shown in the drawing but which is located beyond the valve 23, the mechanism of Fig. 2 will cause the operation of the bellows member II as a pump only when the gas pressure within the bellows 4| is in excess of a certain critical value, and, conversely, that the maintenance of a uniform given gas pressure in connected through theport 43 and pipe45; to an intake valve furnishing gas under pressure, with an escape valve and a pressure gauge (these acce'ssories not being shown in the drawing) so that the pressure within the space 44 may be maintained at the value which will effect the maintenance of the desired pressure upon the liquid in the closed vessel beyond the valve 23.

, In normal operation, the gas pressure within the bellows member 4| will be maintained uniform, so as to maintain uniform pressure upon the liquid beyond the valve 23. 'Butfa change in the latter pressure can be effected, if desired,

' by changing the gas pressure in the bellows member 4|. An increase in the larger immediately causes the mechanism to operate to increase the pressure on the liquid. On the other hand, a lowering of the gas pressure within the bellows-;mem-'- ber 4| does not immediately cause a reduction in the liquid pressure beyond the valve 23 because this valve is heldclosed by that pressure. But

- the polymerization of the liquid in the vessel beyond valve 23. isconstantly causing contraction in the volume" of that liquid, and the resulting-reduction in pressure will presently lower the pressure therein to the desired new value, at

- vided by liquids ofthe type for which the mechaa variable play under constant pressure. 'A par-- which it will thereafter be held by the operation of the mechanism.

} The mechanism shown in Fig. 2 is thus, in effect, an adjustable compressible connecting rod.

The purpose of the plug |6 (Fig. 1) to re- 5 duce the chance bf stagnation of the liquid within the bellows member II. By reducing the liquid capacity of the bellows member H, the plug reduces the duration of stay of a given portion of, liquid within the bellows member By effecting the entrance of the liquid near the bottom of the bellows member II and directing its travel upward through an annular space, a direct, nonof the invention have been shown and those skilled in the .art will understand that numerous mechanical equivalents can be employed and the design of the apparatus varied considerably without departing from the spirit of the invention. Means other than the cam 3| could readily be employed for raising the weighted 'end of the lever member 26 in Fig. 1. Likewise, the compressible connecting member of Fig. 2 could be used as a compressible piston rod rigidly attached to or forming a continuation of the piston |2 of Fig. 1 and actuated by a rigid connecting rod or other means of giving reciprocating motion.

The mechanism of the present invention provides an automatic device for maintaining a substantially constant hydrostatic pressure upon the liquid contained in a mold or other vessel of fixed volume and, in its specific application to the polymerization of organic liquids which contract in volume during polymerization, it serves also to bring into such a mold, under pressure, incre-' merits of polymerizable liquid suflicient to make up for the contraction and thereby to keep the mold completely filled throughout the polymerizati'on. The magnitude of the hydrostatic pressure applied by the mechanism is closely adjustable byvarying the weight applied to the lever arm or by varying the pressure of gas maintained in the bellows member. 4|..

-The liquid handled by the apparatus passes directly through its ports and bellows in such a manner as to expel air. The mechanism is free from sliding metal-to-metal contacts by which 1 the liquid being-handled might be contaminated and which would require for satisfactory operation a lubricatinga'ction whichcannot be proni'sm has been particularly designed. There are 7 no packiiigs, stufling boxes, or release valves, and

the mechanism requires no accumulator for the maintenance of pressure. The mechanism gives ticular advantage of the apparatus is that it contains, in'those parts through which the liquid passes, no .zones of stagnation or dead spots in which a polymerizable liquid could remain long enough-to undergo an objectionable polymeriza'-' tion which might interferewith the functioning of the device.

The present inventionthus provides mama-1 ratus meeting the aforementioned requirements as a pressure-maintaining and feeding device for :76

- stricting said piston member to vertical moveuse in connection with the polymerization of organic liquids in accordance with such process as that set forth in the aforementioned .United States Patent 2,057,674.

As many apparently widely diilerent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that, the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

We'claim:

1. An apparatus comprising the combinationof a vertically disposed bellows member, a piston member forming a liquid-tight enclosure at the lower end of said bellows member, a stationary block forming a liquid-tight closure at the upper end of said bellows member, a plug carried by said block and occupying a substantial part of l the space within said bellows member but having length and width, respectively, less than the length and width of said bellows member, an intake port extending from the lower end of said plug through said plug and through said block, a check valve in said intake port permitting flow of liquid onlyinto s'aid bellows member, a discharge port extending through said block from a point within said bellows member and outside of said plug, a check valve in said discharge port permitting flow of liquid only out of said bellows member, means for guiding and resaid block and occupying a substantial part of the space within said bellows member but havin length and width, respectively, less than the minimum length and width of said bellows member,-an intake port extending from the lower end of said plug through said plug and through said block, a check valve in said intake port permitting flowof liquid only into said bellows member, a discharge port extending through said block from a point within said bellows member and .outside of said plug, a check valve in said discharge port permitting flow of liquid only out of said bellows member, means for guiding and restricting said piston member to vertical movement only, and means for actuating said piston member. v I

CHARLES M. FIELDS. REUBEN T. FIELDS. 

